1. Field of the Invention
This invention relates generally to circuits for accomplishing convergence of electron beams on display panels of color cathode ray tubes, and more particularly, is directed to a circuit used with a color cathode ray tube for correcting dynamic misconvergence of electron beams therein so as to cause the color cathode ray tube to display fine images of high quality.
2. Description of the Prior Art
For the purpose of correction of dynamic misconvergence of electron beams in the horizontal direction caused on the display panel of a color cathode ray tube of the in-line type, such circuits as shown in FIGS. 1A and 1B in the drawings have been proposed. The circuit shown in FIG. 1A is used for correcting the dynamic misconvergence in the horizontal direction appearing at every horizontal period. In this circuit, a voltage of parabolic waveform having the horizontal period and a voltage of saw-tooth waveform having the horizontal period are mixed in a mixer 1H, and a mixed voltage obtained from the mixer 1H is supplied through an amplifier 2H to a coil 3H provided for correcting the dynamic misconvergence in the horizontal direction appearing every horizontal period on the display panel of the color cathord ray tube. With such an arrangement, the condition of electron beam convergence in the color cathode ray tube can be adjusted between the situation where an electron beam for stimulating a phosphor provided on the display panel for emitting red light (hereinafter referred to as a red beam) is shifted to the left on the display panel as shown in the left side of FIG. 2A and the situation where the red beam is shifted to the right on the display panel as shown in the right side of FIG. 2A by means of varying the amplitude of the voltage of parabolic waveform having the horizontal period. The condition of electron beam convergence can be adjusted also between the situation where the red beam is shifted to the inside on the display panel as shown in the left side of FIG. 2B and the situation where the red beam is shifted to the outside on the display panel as shown in the right side of FIG. 2B by means of varying both the amplitude and polarity of the voltage of saw-tooth waveform having the horizontal period.
On the other hand, the circuit shown in FIG. 1B is used for correcting the dynamic misconvergence in the horizontal direction appearing at every vertical period. In this circuit, a voltage of parabolic waveform having the vertical period and a voltage of saw-tooth waveform having the vertical period are mixed in a mixer 1V, and a mixed voltage obtained from the mixer 1V is supplied through an amplified 2V to a coil 3V provided for correcting the dynamic misconvergence in the horizontal direction appearing every vertical period on the display panel of the color cathord ray tube. With such an arrangement, the condition of electron beam convergence in the color cathode ray tube can be adjusted between such a situation as shown in the left side of FIG. 2C and such a situation as shown in the right side of FIG. 2C by means of varying the amplitude of the voltage of parabolic waveform having the vertical period. The condition of electron beam convergence can be adjusted also between such a situation as shown in the left side of FIG. 2D and such a situation as shown in the right side of FIG. 2D by means of varying both the amplitude and polarity of the voltage of sawtooth waveform having the vertical period.
Incidentally, through FIGS. 2A to 2D showing various situations of the dynamic misconvergence in the horizontal direction as mentioned above, R, G and B indicate the positions on the display panel of the red beam, an electron beam for stimulating a phosphor provided on the display panel for emitting green light (a green beam) and an electron beam for stimulating a phosphor provided on the display panel for emitting blue light (a blue beem), respectively.
With the previously proposed circuits as mentioned above, since the positions of the electron beams on the display panel are shifted at both the left and right sides of the display panel by either one of the variation of the amplitude of the voltage of parabolic waveform having the horizontal period and the variations of the amplitude and polarity of the voltage of saw-tooth waveform having the horizontal period on the occasion of adjustment for correcting the dynamic misconvergence in the horizontal direction appearing every horizontal period, as understood from FIGS. 2A and 2B, it is necessary for correcting the dynamic misconvergence in the horizontal direction appearing every horizontal period at both the left and right sides on the display panel to establish a tracking relation between the adjustment by means of varying the amplitude of the voltage of parabolic waveform having the horizontal period and the adjustment by means of varying the amplitude and polarity of the voltage of saw-tooth waveform having the horizontal period. Further, since the positions of the electron beams on the display panel are shifted also at both the top and bottom sides of the display panel by either one of the variation of the amplitude of the voltage of parabolic waveform having the vertical period and the variations of the amplitude and polarity of the voltage of saw-tooth waveform having the vertical period on the occasion of adjustment for correcting the dynamic misconvergence in the horizontal direction appearing every vertical period, as understood from FIGS. 2C and 2D, it is necessary for correcting the dynamic misconvergence in the horizontal direction appearing every vertical period at both the top and bottom sides on the display panel to establish a tracking relation between the adjustment by means of varying the amplitude of the voltage of parabolic waveform having the vertical period and the adjustment by means of varying the amplitude and polarity of the voltage of saw-tooth waveform having the vertical period. As a result, the adjustments for correcting the dynamic misconvergence in the horizontal direction require very complicated and troublesome control, and moreover the misconvergence at each of four corners of the display panel where the electron beams are affected with all the adjustments is substantially unable to be eliminated.